Electrical amplifying system



ELECTRICAL AMPLIFYING SYSTEM Filed Aug. '9. 1927 i EP/Q INVENTOR Walter J Bro wn ATTO'RNEY iatented Mar. 15, 1932 "UNITED s A 1 TBS;

V WALTER JOHN snow-N, or nnooKLANns, ENGLAND, .assrenon To Assocurnnmm- TRIGAL INDUSTRIES LIMITED, OF LONDON, ENGLAND, A CORPORATION OEENGLAND q "ELECTRICAL AMPLIrYmG srsrim Application med August 9, 1927, Serial no. 211,658, and in Great Britain September 10,1926.

My invention relates to electrical amplifying systems, and particularly to systems of thetype in which-a plurality of thermiomc;

valves are utilized for diiferent'types ofam plification, as, for example, radio receiving" systems in which certain valves amplify the voltage of the signalat high frequencies, and

other valves supply relatively heavy currents to a sound reproducing device such as a loud m. speaker. v q j A system j of the kind referred to usually comprisesja plurality of amplifying stages that require onlya-small' amount of anode supply current, and an output, or power, stage employing a valve or valves in which the volt.-

age amplification is usually low but the anode current consumption is high.

Since the amplification of the output or power stage is low, a small amountof devig ation from true constancy of voltageof its anode supply does not produce any appres ciable efiect in a loud speaking telephone and, consequently, the current for this stage may be supplied through a filter of large current capacity,but of relatively low/attenuation. The earlier amplifying valves, suchas those used for high frequency amplification and for demodulation, on the other hand, 'owingto the fact that there may be a very large degree of amplification betweenithem and the power stage, must be supplied with anode current at a voltage which differs from a constant voltage by only very minute variations. ,In other words, the amplifying stages, a particularly ..5 those early in sequence, must be. supplied through a filter of very great attenuation, although its current capacity'may be relative ly small. weight of an, electrical filter increase'with its current capacity and also with the degree of attenuation required. Consequently a single filter to deliver the current required for the output stage, while at the same time having the degree of attenuation required in order n that it may deliver current to the preceding stages without causing undesirablenoise or hum in the loud speaker, is a somewhat large, heavy and expensiveapparatus. p

n It is ,accordinglyan object of my invention to provide means for economically supplying The mechanical dimensions and power to the variousthermionic valves com-f prised in an amplifying system. I T My invention also'includes the combination of two'electrical low-passfilters, one having 7 PATEN OFFICE-3+ In amplifying instruments employing my invention the'rislrrof retroactive couplin be tween the last stage of amplification an one or more stages earlier in sequence, by an'im pedancecommon to both stages, is alsominimized., r} H i V I Accordingly to myinvention, in a wireless or like amplifying instrument employing a plurality of. thermionic valvesijforsupplymg audio frequency'current to theloudspeaker,

the last orrpowerstage of amplification requiring a large anode current is'fed through a. filterhaving' a relatively low attenuation and a relatively high current capacity, andanother stage or stages earlier in sequenceand requiring relatively small anode current is or are fed from anotherfilter of high attenuation-and lowcurrent capacity,

In carrying outfmy invention as applied a wireless receiving instrument, {consisting of a detector valve,.resistance ortransformer coupled to tWo voltage amplifying; valves, which amplifying valve mayalso be resistance or transformer coupled' to one another, and a power valve which is resistance or transformer-coupled to :the last one of the voltage I amplifying valves, the last or powenvalve may be supplied with anode current from a filterof a singleostage comprising a capacitor 7 in shunt and a choke coil in series I The detector and voltageamplifying apparatus mayall be fed from a common filter of 2, 3', or ,4 stages, each consisting of capacity in arallel and inductance in series, H V n a receiver of the kind described great sensitivity and economy in anode current is obtained by employing valves havinglahigh voltage amplification factor, sayv about 30 or 40, the first three positions, and by employing values of resistan Qqof the order of half a megohm in the anode circuits. On the other hand itis customary to employ i in the last or output stage a valvehaving a 1 low voltage amplification factor, say between 3 and 6, and a correspondingly high anode current, in order to deliver sufficient power to the loud speaker without distortion.

In such an instrument, the current required by the last or power Valve may be of the order of 25 milliamperes. On the other hand the current required by the detector and amplifyingvalves rarely exceeds a quarter of a milliampere'per valve. Thus thetotal current taken by the detector and two voltage amplifying valves may very probably not exceed three quarters of a niilliampere. Consequently, the filter apparatus for supplymg these three valves may be made qulte small,

notwithstanding the high degree of attenua-f tion which is necessary. .Owing to the large current required by the last or power valve a single stage filter for this valve will be of much the same mechanical dimensions as the multi-stage filter for the other three valves. If, however, 7 all the valves were supphed from a common filter the mechanical dimensions of such filter and its weight and consequent cost, would be muchgreater than those of the two filters provided accordingto my invention. r

I Among the novel featuresof my invention are those particularly set forth in the appended claims; The invention itself, however, both as to its-organization and its methods of operation, together with further ob jects and advantages thereof, will best be understood from 'a' consideration of the following description of certain specific embodiments, taken in connection with the accompanying drawings, in which:

F igure 1 is a diagrammatic view of a re ceiving instrument for Wireless telegraphy or telephony comprising'a preferred emb0d1- ment of my invention.

r Fig. 2 is a'similar'view of a radio receiver comprising a modified form of my invention.

Fig. 3 is a view in'perspective of an iron core for a choke coil, or inductor, suitable for use in connection with the apparatus shown in Figs. 1 and 2, and

Fig. 4 is a diagrammatic view'of a modified form of filter.

In all of the above referred to views like reference numerals indicate like parts where applicable throughout. The receiver'illustrated in Fig. 1 consists of a tuning arrangement 1 which is connected to an aerial and earth and to the control elec others are voltage amplifying devices and may act at radio frequency or audio frequency according to the position in sequence of the detector valve.

Although I have described the valves 24 and 6 as a detector and voltage amplifying devices, my invention is not to be restricted. by such a description. The first valve shown may be aradio frequency amplifying valve,.- as may also be thevalves 4 and 6, or the latter valves may be comprised in the intermediatefrequency amplifying stages of a superheterodyne. The said valves 2, 4 and 6 are simply shown as illustrative of anyvalves employed for voltage rather than for current or. poweram'plification.

The three valves 2, 4, and 6 consume only a small amount of anode current, which may Y reach a total of from 3 to 6 milliamperes.

The valve 8, on the other hand, whichis con- I nected to the loud speaker 9, is of thetype known as a powervalve, and may consume'a' current'as great as 25 mlll amperes or even greater. 1 I V The anode circuits of all of the valves are supplied from a source 10 0f uni-directional currenti The source 10 may be the direct current mains,or it may be a'rectifying arrangement, connected to alternating-current mains, with an appropriate reservoir condenser included in the output circuitthereof."

a smoothing condenser '14 to the common cathode conductor 11 and to a common anode feed conductor 15, from which the anode cir .cuits of the valves 2, 4 and 6 are fed; a The choke coil 13 is constructed if desired'on a similar iron core to that utilized for the choke coil 12, but with less turns of thicker wire, so that its current-carryingcapacity is considerably greater than that of the choke coil 12, but its impedanceto alternating current of any particular frequency is lower than that of the choke coil 12. V

The second end of the choke coil 13 is connected through a large smoothing condenser 16 to the common cathode conductor 11 and through the loud speaker 9 to the anode of the valve 8. p 1

The choke coil 12 and smoothing condenser 14 aredesigned so that the frequencies of variation of potential which maybe present in the source 10 are attenuated to such a point that the potential variations which are ap; plied to the anode of valve 2 are, when amplified by the amplifier, not made materially evident by theloud speaker 9.

lio

.The choke coil 13 and condenser 16 on the other hand are designed to attenuate the potential variations of the source 10 to a less extent, since this choke coil and condenser are connected only to the anode circuit of the last valve and potential variations therein are therefore not amplified.

The arrangement illustrated in Fig. 2 is generally similar to that illustrated in Fig. 1. A separate reservoir condenser 18 is however connected across the terminals of the source 10 and a potential divider 19 is also connected across these terminals. The end of the choke coil 12 is so connected to an adjustable point 20 on the potential divider that the potential supplied to the amplifying and detecting valves 2, 4 and 6'may be lower than that applied to the anode of the valve 8, and may be readily adjusted independently thereof.

The choke coils 12 and 13 may be conveniently constructed upon a laminated core of the shape illustrated in Fig. 3. In order-to facilitate the construction of these choke coils the essential dimensions are given b way of example only. The air gaps 21 an 22 in the magnetic circuit may each be 1 mm. wide. The thickness of the core in a direction transverse of the laminations may be 2 cm. The width of the middle limb 24 of the core may be 1.9 cm., and the width of the other limbs 25, 26, 27, 28, 29 and 30 may be 1.25 cm. For the choke coil 12 (Figs. 1 and 2) the core described may be wound with 30,000 turns of insulated copper wire 0.002 in diameter. The choke coil 13 in Figs. 1 and 2 on the other hand may be wound with 4,500 turns of insulated Wire 0.0068 in diameter. Thus for the choke coil 12 the magnetomotive force when 3 milliamperes are flowing through it will be 90 ampere turns, while when 25 milliamperes are flowing through the choke coil 13 the magnetomotive force in this choke coil will be 112 ampere turns, and its inductance in these circumstances will be of the order of 25 henrys. The total weight of each of the choke coils constructed as described is about 1 lb. 10 ozs.

The smoothing condensers 14 and 16 illustrated in Fig. 1 may each be of 2 microfarads capacity.

If the amplifying stages of the amplifier or receiver have very reat over-all amplification it may be desirable to incorporate several stages of high attenuation in the filter which supplies the amplifying stages of the receiver with current, as shown in Fig. 4:. For this purpose additional choke-coils 31 and 32 and condensers 33 and'34 are added to increase the attenuation of the filter which is connected to the amplifying valves.

It will be appreciatedthat the two filters may both be fed from a common rectifier in cases where the supply is taken from alternating current mains, or they each may be fed from an independent rectifier. Where or one or both may :more potential dividers which are connected direct current mains are used both filters may, of course, be connected directly to the mains be connected to one or direct y across the mains.

It will be appreciated by those skilled in the art that the above description is given by way of example only, and that many modifications may be made without dleparting from the scope of the invention. y invention, therefore, is not to be limited except insofar as is necessitated'by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. In radio apparatus, a plurality of thermionic devices relatively sensitive to anode voltage fluctuations, at least one thermionic 1 device relatively insensitive to anode volt e fluctuations, a source of anode otential su ect to fluctuation, a filter having relatively igh attenuation low current capacity interposed between said source and said first mentioned devices, and a filter having relatively low attenuation'and high current capacity interposed between said source and said last mentloned device. I i

2. In an amplifying system, a source of potential subject to fluctuations, a thermionic device relatively sensitive to anode potential variations connected thereto through a filter having high attenuationfand low current-L carrying capacity, and a second thermionic device relatively insensitive to anode potential variations connected .to said source through a filter having low attenuation and high current-carrying capacity, said filtering devices having an element in common.

In testimony whereof, I have hereunto sub-= scribed my name this twenty-first day of July, 1927. l i

. WALTER JOHN BROWN. 

